1. Field of the Invention
This invention relates to the process of applying finely divided material to tacky surfaces. More particularly this invention relates to image reproduction systems, and still more particularly to image reproduction systems involving the application of toner particles over a tacky surface to develop a latent image.
2. Description of the Prior Art
The advent of electrophotography and wide acceptance of electrostatic reproduction methods have resulted in a large number of processes and devices to apply toner particles on a charged surface. Methods of applying electroscopic toner by sprinkling or dusting, cascading, transferring, brushing, etc., are well known.
In the graphic arts area, powdered materials are sometimes applied to tacky surface areas to make images and particularly multicolor images such as described in U.S. Pat. No. 3,649,268, and the patents referred to therein. Following imagewise exposure of such a film, the latent image is developed by the application of toner particles on the surface, and subsequent removal of the particles from nonimage areas by brushing away loose toner, as disclosed in U.S. Pat. No. 3,060,024. It has also been known in the art to use a small pad having a handle on one side and a thick pile such as lambs wool on the other to apply and distribute the toner over the latent image bearing surface. The pad is dipped in a dish containing a supply of toner; it is then rubbed lightly and repeatedly in an S type path over the latent image bearing surface. Since there are areas of different degrees of tackiness on this surface, toner particles adhere on the tacky sections to develop an image. The shearing force present during the application of the toner because of the sideways motion of the pad often results in a streaked appearance particularly in large solid areas in the final image.
To avoid this, the toner may be applied by patting a pad dipped in toner all over the surface and then using the pad to rub the surface with an S type motion as before. This tends to eliminate streaks, however, the patting motion generates an objectionable dust cloud, and requires special measures or equipment control. In addition, there is no way to control the uniformity and amount of applied toner, which results in variations on the top density over areas of the image, especially when the method is used by an inexperienced operator.
Finally, the use of a rotating, or a rotating and oscillating cylindrical brush to obtain embedding of toner particles in powder receptive areas is suggested in U.S. Pat. No. 3,754,912. This method employs a shearing or brushing force in the application of toner. What is needed is a convenient, speedy process whereby a uniform layer of toner may be applied reproducibly over a surface to develop a uniform image without depositing a great excess of toner or generating a dust cloud, nonuniform solid areas, streaks, mottle, or variable top densities from operator to operator.